A wide variety of display devices have been designed and manufactured for use in merchandising shelved products to consumers. One of the major problems associated with storing and displaying shelved products for sale to consumers and, in particular, shelved products requiring refrigeration in display coolers and other types of cold vaults, is the inefficient use of available shelf space, particularly, the vertical space available between adjacent shelves. Although various product display devices have been designed to alleviate this particular problem such as the two-tier systems disclosed in U.S. Pat. Nos. 4,593,823 and 4,801,025, such units are not always adaptable for use within refrigerated display coolers since the spatial dimensions associated with existing coolers vary from one refrigerated unit to the next. Also, such prior art two-tier shelving units are tied to each other and such systems are not always easily maneuverable within a particular cold vault, particularly, when such units are loaded with product. The relative stability of existing two-tier systems is also of some concern particularly in light of the advent of the larger product containers commonly used, for example, in the soft drink industry. The wide use of multiple product container heights also requires the height between vertically spaced shelving to be adjustable to accommodate such product height differences, a feature not always possible with existing two-tier systems. It is therefore a principal aim of the present invention to obviate many of the disadvantages and shortcomings associated with the known prior art devices and to provide a shelf support structure which is compatible for use with many of the existing refrigerated display coolers, which is both width and depth adjustable, and which enables a user to form a multi-tier shelf system within a refrigerated cooler thereby maximizing usage of the vertical space available between adjacent product merchandising units.